The matrix voice is depending on the version only a microphone. Snips is an independent software platform for local voice assistants where the matrix voice is only one of many microphone arrays you can use to build your own voice assistant. The bare minimum you need for snips is a raspberry pi 3 and one of the old Playstation Eye cameras which have a 4 mic array and you can get them for under 10€ on eBay. Another popular choice would be to use a respeaker 2 mic or 4 mic array for the pi which are quite cheap too.
There is actually quite a few people including me using snips and Openhab in conjunction. A quite recent tutorial is this one here on the Forum:
And even over on the Snips Forum there is a few Openhab Users participating.
It’s a great system I I can fully recommend it.
Best regards Johannes